Sensitive materials generally consist of a support which has electrical insulating properties and a photographic layer. Considerable electrostatic charge accumulates as a result of contact friction with the surface of a similar or different type of material or on peeling during the manufacture or use of the sensitive material. Such an accumulated electrostatic charge causes various problems, the most serious of which is the formation of spots, or tree or feather like lines, due to the discharge prior to development processing, of the electrostatic charge which has accumulated during exposure of the photosensitive emulsion layers or during the development processing of the photographic film. These marks are known as static marks and their presence results in a marked reduction in the quality of a photographic film and, depending on the actual case, it can completely destroy the commercial value of a given material. For example, such marks can easily lead to faulty conclusions with potentially serious consequences if they appear on X-ray films used for medical or industrial purposes. The phenomenon becomes first clear after the completion of development. Furthermore, there are secondary problems in that the accumulated electrostatic charge may cause dust to stick to the surface of the film, or lead to problems with uneven coating.
Such electrostatic charges often accumulate during the manufacture and use of sensitive materials and they may be produced, for example, by contact friction between the photographic film and rollers during the manufacturing process, or as a result of separation of the support surface from the emulsions surface on winding and unwinding the film. Furthermore, electrostatic charges can also be generated by the separation of the emulsion surface from the base surface when winding and cutting photographic film in the finishing process, and as a result of X-ray film making contact with, and separating from, mechanical parts or fluorescence sensitizing papers in automatic cameras. Electrostatic charges can also be generated by contact with packaging materials, etc. The static marks on sensitive materials brought about by the accumulation of such electrostatic charges becomes more of a problem as the speed of the sensitive material increases and as the processing rate is increased. In more recent times in particular, the problem of static marks has become more acute as a result of the increased speed of the sensitive materials and the increased opportunity for vigorous handling such as high speed coating, high speed shooting, and high speed automatic development processing.
The addition of antistatic agents to sensitive materials for preventing these problems due to static electricity from arising is clearly desirable. However, the antistatic agents which can be used in sensitive materials are generally not the same as those used in other applications due to various limitations imposed by the sensitive material. As well as having excellent antistatic properties, the antistatic agents used in sensitive materials must have no adverse effect on the photographic characteristics of the sensitive material, such as speed, fog, graininess or sharpness, etc. These antistatic agents must not have an adverse effect on the film strength (such that they must not result in the film becoming liable to damage by wear or scratching), they must not have an adverse effect on the anti-stick properties of the sensitive material (such that they do not cause the material to adhere to the surface of similar photographic material or other materials), they must not cause the processing baths of the sensitive material to become exhausted, they must not contaminate transport rollers and they must not reduce the strength of adhesion between the various layers which make up the sensitive material. Clearly many limitations are imposed on the application of antistatic agents to sensitive materials.
In one method of overcoming the problems caused by static electricity, the electrical conductivity of the surface of the sensitive material is increased so that the static charge is dispersed quickly before it is able to accumulate and discharge.
Hence, consideration has been given in the past to methods by which the electrical conductivity of the support and the various coated surface layers of the sensitive material can be raised, and attempts have been made to use various hygroscopic substances, water-soluble inorganic salts and various surfactants and polymers, etc., to achieve this goal.
Among these materials, surfactants that are of importance from the point of view of their antistatic performance include the anionic, betaine and cationic surfactants and the nonionic surfactants as disclosed in JP-B No. 48-l7882 (the term "JP-B" as used herein refers to an "examined Japanese patent publication"), JP-A No. 52-80023 (the term "JP-A" as used herein refers to a "published unexamined Japanese patent application"), in West German Pat. Nos. 1,422,809 and 1,422,818, and in Australian Pat. No. 54,441/1959, etc., are well known.
However, these substances are specific with respect to the type of film support and photographic composition employed. Those which provide good results with certain specified film supports, photographic emulsions and other photographic structural elements may have no antistatic effect at all with regard to other film supports and photographic structural elements. Even if these substances do have excellent antistatic properties, they may have an adverse effect on photographic characteristics of the photographic emulsion, such as speed, fog, graininess or sharpness, etc., or they may cause contamination of the development processing baths, or they may cause the material to stick to rollers, etc. Thus, it is very difficult to make use of these substances in sensitive materials.
Furthermore, the antistatic techniques employing nonionic surfactants closely depend on the coating agents which are used conjointly. Rapid progress has been made with respect to the antistatic performance of these materials, but more consideration must be given to contamination of development processing baths and transport rollers by these antistatic materials which can cause serious film problems.
For example, the ethylene oxide adducts of phenol-formaldehyde condensates disclosed in JP-B No. 5-9610 provide excellent antistatic performance, even when they are used conjointly with various coating agents. However, the problems due to contamination during the course of development processing are not resolved with the method disclosed in the patent.
Furthermore, sensitive materials which contain specified anionic surfactants and polyoxyethylene-based nonionic surfactants have been disclosed in JP-A No. 53-29715 but, as in the case of JP-A No. 51-9610 mentioned above, there is no improvement with respect to the problems which arise as a result of contamination of the development processing baths and transporting rollers.
There are methods of overcoming these contamination problems with the use of the polyoxyethylene-based nonionic surfactants, the anionic surfactants which contain polyoxyethylene groups, and the fluorine-containing anionic surfactants disclosed in JP-A Nos. 60-76741 and 60-76742.
On the other hand, in recent years the speed of development processing of sensitive materials has been increased using high temperature rapid processing systems and processing times have been greatly reduced with the automatic development machine processing of various types of sensitive materials. Development baths with which sufficiently high speed can be realized in a short period of time and sensitive materials which have excellent development properties and which have to residual coloration even with short processing times, and which dry quickly are required for high temperature rapid processing. A drying zone is incorporated into most automatic developing machines. If the drying properties of the sensitive materials are poor, then a higher drying capacity is required and the size of the machine is inevitably increased. Furthermore, more heat is generated and this effects temperatures in the room in which the automatic developing machine is housed in.
Work has been directed at providing sensitive materials which dry as quickly as possible in order to overcome these problems. The methods generally used involve adding a suitable amount of a film hardening agent prior to, or during the coating of the sensitive material in order to minimize swelling of the emulsion layers and the surface protective layers during the course of development, fixing and water washing. Thus, the water content of the sensitive material is reduced prior to the commencement of drying. It is possible to speed up the drying process in this way by using large amounts of a film hardening agent, but development slows down and speed is decreased by the increased hardness of the film. In addition, covering power is reduced, the fixing rate of the undeveloped silver halide grains is reduced, residual coloration is deteriorated and a large amount of hypo is retained in the sensitive material after processing. On the other hand, reduction of the water content of the sensitive material prior to the commencement of drying can be achieved by reducing the amounts of the hydrophilic materials (e.g., gelatin, synthetic polymers, and hydrophilic low molecular weight substances, etc.) which are coated on the sensitive material. Hydrophilic low molecular weight substances are generally added to prevent dry fogging of the silver halide grains during the coating process and the sensitive material is inevitably fogged if these agents are omitted. On the other hand, if gelatin and synthetic polymeric materials which are used as binders for the silver halide grains are omitted, the amount of binder with respect to silver halide grains is reduced and there is an increase in silver content. Reduction in the amount of binder can also lead to a worsening of graininess and variations in speed as a result of flexing and scuffing during the handling of the sensitive material prior to development processing are liable to occur. Thus, even though the drying properties are improved, it is not really possible to reduce the amount of binder because of these problems. Against this background, the provision of a technique which enables a sufficiently high speed to be achieved with a short processing time, which provides excellent mixing and water washing properties, with which there is little residual coloration, and with which drying can be achieved in a short period of time is clearly desirable.
A method in which organic material (for example, gelatin, matting agent, plasticizer, synthetic polymeric material or some other organic substance) which has been coated in the emulsion layer or other hydrophilic layer is washed out in an amount of at least 10% of the total coated weight prior to processing during the course of development, fixing, water washing and drying when the sensitive material is being processed in an automatic development machine, as disclosed in JP-A No. 63-68837 has been developed as a means of resolving these problems with development processing in automatic development machine.
It is thus possible with this method to obtain pictures which have an excellent high covering power while still having a sufficiently rapid drying rate.
However, new problems arise when the method in which large amounts of organic material are washed out into the processing baths during development processing is used conjointly with the antistatic techniques described earlier. This is because the nonionic surfactants which are used as antistatic agents in the sensitive material are washed out in large amounts into the development bath as the organic material is being washed out. Process contamination thus arises with the formation of insoluble material in the development and fixing baths, for example. The bath contaminants accumulate when large amounts of sensitive material are being processed and they adhere to the sensitive material, giving rise to development failure and fixing failure. This has a marked adverse effect on picture quality.
Methods in which use is made of polyoxyethylenebased nonionic surfactants, anionic surfactants which contain polyoxyethylene groups and fluorine-containing anionic surfactants which contain polyoxyethylene groups as disclosed in the aforementioned JP-A Nos. 60-76741 and 60-76742 have been used as a means of overcoming this problem, but it has not been possible to provide simultaneously both excellent antistatic properties and improvement in respect of processing bath contamination (especially fixing bath contamination) even when these techniques are employed.